Ecological and Economic Importance of Bats in Integrated Pest Management

Agricultural insect pests cost the U.S. agricultural industry $33 billion per year in crop losses, and destroy approximately 25–50% of crops worldwide. This trend continues despite an increased use of pesticides in recent decades on farms throughout the world. Broad-spectrum pesticides are dangerous to human health, degrade ecosystem function, upset carefully optimized integrated pest management (IPM) programs, and devastate natural insect predators and parasitoids. In addition, the World Resources Institute estimates that up to 400 agricultural pest species may have evolved some degree of pesticide resistance.

One effort to limit pesticide includes the use of biological control agents, which are living organisms that prey upon pest species. While proven effective in some cases, biological control comes with significant economic costs and typically offers only partial control. Biological control agents are typically non-native species and may have long-lasting negative effects on native biodiversity.

Native generalist predators can effectively serve as agents of biological control. Temperate insectivorous bats are highly effective generalist predators, and studies have documented the presence of many agricultural pest species in their diet. Especially during the summer months, when bats are raising young, female bats consume a significant proportion of their body weight in insects per day. Because they feed within a few kilometers of their roost site and return to the same roost every day, bats may play an important role in local suppression of agricultural insect pests.

We now know that the majority of a bat's diet consists of moths (lepidopterans), beetles (coleopterans), flies (dipterans), cicadas and leaf hoppers, and true bugs (hemipterans). These orders of arthropods include many important agricultural insect pest species. Some prominent examples include the corn earworm moth (Helicoverpa zea), and the cotton bollworm (Helicoverpa zea), the spotted cucumber beetle (Diabrotica undecimpunctata), and the green stinkbug (Acrosternum hilare). A detailed list of insect pests in New Jersey known to be consumed by bats is included in Table 1.

Economic Importance of Bats

Bats provide an important ecosystem service through pest consumption, which is valued at $22.9 billion annually in the United States. The economic benefits of bats are usually estimated by examining the reduction of pesticide use and avoided costs of crop damage. For example, bats in south-central Texas eliminate the need for at least one application of insecticides on cotton fields, and reduce larval damage to crops, resulting in a net benefit of $741,000 per year. However, bats also contribute more subtle indirect benefits. For instance, bats reduce fungal infections of corn, which in turn, reduces negative impacts on the livestock that consumes it. Pesticide reduction also limits environmental damage and human health risk.

Bat-friendly Agricultural Practices

Modifying habitats to support natural insect predators like bats, termed "conservation biological control," has become a valuable component of integrated pest management (IPM) programs. Big brown bats (Eptesicus fuscus) and little brown bats (Myotis lucifugus) are the two species of bat most commonly found roosting in bat houses and man-made structures in New Jersey. Installing bat houses throughout a farm provides quality bat habitat for these species and can attract large maternity colonies if installed correctly.

Another bat-friendly agricultural practice is to support non-crop habitat such as woodlands, ponds, and meadows on the farm. While big brown and little brown bats do well in man-made structures, other species rely heavily on forested habitat. Maintaining tree lines and forest patches with a diversity of vegetation can help provide habitat for forest-dwelling species. Each bat species consumes a slightly different group of insects; therefore, supporting a diversity of bat species will help increase pest control benefits. In addition, avoiding deconstruction of old structures (i.e., barns) in which bats might be roosting, and keeping standing dead trees in place, can help maintain habitat availability for bats.

Conclusion

Researchers continue to use innovative methods to explore the role of bats as biological control agents. Increasing bat habitat on agricultural lands and in residential areas could promote insect suppression, as well as help to conserve these beneficial animals. For further information, please visit our website at wildlife.rutgers.edu or email us at wildlife@njaes.rutgers.edu.

Cooperating Agencies: Rutgers, The State University of New Jersey, U.S. Department of Agriculture, and County Boards of Chosen Freeholders. Rutgers Cooperative Extension, a unit of the Rutgers New Jersey Agricultural Experiment Station, is an equal opportunity program provider and employer.

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